The present invention pertains generally to devices for use as drip irrigation emitters. More particularly, the present invention pertains to drip irrigation emitters that provide a substantially constant drip flow-rate over a wide range of line pressures. The present invention is particularly, but not exclusively, useful as a self-cleaning, pressure-compensating, irrigation drip emitter.
Many plants require sub-surface irrigation for effective growth and function. In particular, for large commercial operations, localized irrigation that is characterized by the administration of water in the vicinity of each plant can effectively conserve water and help prevent soil erosion due to runoff. Further, localized, low-flow irrigation over a relatively long irrigation cycle can result in deep subsurface water penetration which is beneficial for plants.
For many years, drip emitters have been used for delivering localized, low flow irrigation to the roots of plants. Generally, in use, drip emitters are placed in fluid contact with a water feed line such as a half-inch diameter irrigation line. To accomplish localized delivery of water, some drip emitters rely on the use of one or more small orifices to create a drip flow. When used, such an orifice or restriction emitter reduces the water pressure and flow rate in the irrigation line to a lower pressure and lower flow rate for the water as it passes through the orifice. Specifically, the reduced pressure and flow rate is suitable for creating a drip flow.
Unfortunately, simple orifice or restriction emitters often become clogged due to particulates in the feed line or debris that enters the emitter from outside the irrigation line. Further, simple orifice or restriction emitters are not pressure compensating, and consequently, the flow of drips through the simple emitter varies as the pressure in the irrigation line varies. The pressure within an irrigation line may, however, vary for several reasons. For example, the supply pressure may vary over time due to changes in water demand. Also, when long irrigation lines are used, a pressure drop along the length of the irrigation line may occur due to the frictional forces presented by the irrigation line. Further, when irrigation lines are used on hilly terrain, the pressure within the line may fluctuate due to variations in hydrostatic pressure. Consequently, emitters that lack the ability to compensate for pressure variations may cause uneven watering and cause the irrigation system to be hard to control.
Heretofore, drip emitters containing a pressure compensating flexible membrane have been disclosed. In these emitters, one side of the membrane is exposed to irrigation line pressure, while the opposite side of the membrane is exposed to a reduced pressure. For example, the reduced pressure can be created by forcing a portion of the water from the irrigation line through a restrictor or labyrinth. This pressure differential on opposite sides of the membrane causes the flexible membrane to deform. In particular, the higher line pressure can be used to force the flexible membrane into a slot where reduced pressure water is flowing. As the line pressure increases, the membrane will be pressed further into the slot, decreasing the effective cross-section of the slot and thus restricting flow through the slot. As described further below, the result is a constant flow through the emitter over a range of line pressures. Unfortunately, the slot is subject to clogging in the same fashion as the simple orifice emitter. Further, the membrane is required to form a seal with the edge of the slot confining flow to the slot. Unfortunately, particulate buildup may also interfere with the membrane seal causing non-uniform flow.
One attempt to solve the problems associated with particulate buildup in a pressure compensating emitter uses the reduced-pressure water from the labyrinth to clean the slot and sealing surfaces during initial pressurization of the irrigation line. In particular, such an emitter is disclosed by Miller in U.S. Pat. No. 5,628,462 which issued May 13, 1997, entitled xe2x80x9cDrip Irrigation Emitter,xe2x80x9d in which a chamber is created between the slot and the membrane. For the emitter disclosed by Miller, during initial pressurization of the irrigation line, while the membrane is only slightly deformed, the chamber is flushed with reduced-pressure water delivered from the restrictor or labyrinth. As the line pressure increases, the membrane deforms, sealing off the chamber from reduced pressure water, and restricting flow through the slot. Unfortunately, the reduced pressure water may be ineffective in adequately cleaning the slot and membrane.
In light of the above it is an object of the present invention to provide devices suitable for the purposes of providing a constant drip flow in response to a varying line pressure without becoming clogged. It is another object of the present invention to provide a self-cleaning drip emitter that uses water that is not pressure reduced to self-clean the membrane and slot. Yet another object of the present invention is to provide an irrigation dripper which is easy to use, relatively simple to manufacture, and comparatively cost effective.
The present invention is directed to a self-cleaning, pressure compensating drip emitter that is bonded to the inside wall of an irrigation line. The emitter includes an enclosing sidewall that extends from the inner wall of the irrigation line to a cover. The sidewall is formed with a ledge that is located between the cover and the inner wall of the irrigation line. A flat, flexible membrane having two opposed sides is positioned between the ledge and the cover. A fluid chamber surrounded by the sidewall is thus created between one side of the membrane and the inner wall of the irrigation line. Further, an antechamber surrounded by the sidewall is thus created between the ledge and the cover. The cover contains one or more holes to allow fluid communication between the lumen of the irrigation line and the antechamber. Consequently, one side of the membrane is in fluid communication with the fluid chamber and the other side of the membrane is in fluid communication with the lumen of the irrigation line.
Further, an outlet is provide for the fluid chamber to allow fluid to pass from the fluid chamber to the outside of the irrigation line. Within the fluid chamber, the outlet has an aperture where fluid can enter the outlet from the fluid chamber. The outlet is further formed with a valve seat surrounding the aperture, and the valve seat is formed with a slot. A valve may be mounted on the flexible membrane for cooperation with the valve seat to form a seal, and for cooperation with the slot to restrict a portion of flow within the slot.
Two passageways allow fluid from the lumen of the irrigation line to enter the fluid chamber for subsequent exit from the irrigation line through the outlet. The first passageway, or flushing passageway, is a direct passageway from the lumen of the irrigation line to the fluid chamber. Importantly, the flushing passageway first enters the antechamber from an entrance located in the sidewall between the ledge and the cover. The second passageway, or operational passageway, is formed as a labyrinth between the lumen of the irrigation line and the fluid chamber. Importantly, the operational passageway enters the chamber from an opening in the sidewall that is located between the ledge and the aperture of the outlet. The operational passageway reduces the pressure of the fluid from the irrigation line to create a drip flow during steady-state operational flow conditions.
During operation, fluid is supplied to the irrigation line from a fluid source. Initially, the pressure within the irrigation line is low as the fluid from the source flows into the irrigation line, displacing trapped air. Gradually the pressure in the line increases until a steady-state pressure is established in the irrigation line. During the initial pressurization of the irrigation line, the pressure on both sides of the flexible membrane is low and the flexible membrane does not deform or block either of the passageways. Consequently, fluid from the direct flushing passageway passes into the antechamber through the sidewall at the entrance. From the antechamber, the fluid passes between the ledge and the membrane and enters the fluid chamber where it effectively flushes any particulates from the chamber, valve seat, aperture, slot and outlet to the outside of the irrigation line.
As the pressure within the irrigation line increases, the differential pressure between the line pressure on one side of the membrane and the reduced fluid chamber pressure on the opposite side of the membrane becomes significant. As this differential pressure begins to increase, several events take place. First, under relatively small differential pressures, the membrane is forced against the ledge of the chamber creating a seal which prevents the fluid from flowing through the flushing passageway and entering the fluid chamber.
Next, further increases in pressure differential will cause the membrane to deform and collapse into the chamber, causing the valve to contact the valve seat. This partial blocking of the chamber and aperture will reduce the flow of fluid from the operational passageway through the chamber and into the outlet. Subsequent increases in pressure differential will cause the membrane to further deform resulting in the valve forming a seal with the valve seat. At these pressure differentials, flow is limited to fluid from the operational passageway flowing into the chamber and entering the outlet through the slot in the valve seat. Additional increases in pressure differential will force the valve into a portion of the slot, thereby partially restricting the flow of fluid through the slot.
In summary, as the pressure in the irrigation line increases, the differential pressure across the membrane will increase. As the differential pressure across the membrane increases, the membrane and valve will cause a series of restrictions within the chamber, with each restriction causing a further reduction of flow through the outlet. At the same time, the increases in line pressure will cause the pressure of the fluid entering the chamber from the operational passageway to increase. However, constant flow through the outlet is achieved in spite of the varying line pressure because the increased pressure in the operational passageway is offset by the restrictive effects of the membrane and valve.